When a sprocket used to drive or support a linked conveyor belt wears, it must be removed from the shaft on which it is mounted and replaced. In abrasive environments, sprocket wear is especially exacerbated. The task of replacing the worn sprocket can be time-consuming, especially if the shaft has to be separated from the conveyor frame so that the worn sprocket can be pulled off the shaft and a new one slid into position. Split sprockets having multiple sections were developed to alleviate the problems encountered in changing sprockets. The multiple sections can be disengaged and removed from the shaft without dismounting the shaft.
B. G. Mills, in U.S. Pat. No. 184,540, shows a sprocket wheel with a removable portion for easy replacement on a shaft. The removable portion dovetails with the rest of the sprocket wheel in a tight fit. The thickness and mass of the wheel section with respect to the removable portion, along with the closely machined dovetail joint, are crucial to retaining the removable portion in place. Because removal requires that the removable portion be driven from its tight fit, such a sprocket wheel is not feasible in situations requiring a number of closely spaced sprocket wheels on a shaft.
A sectional gear wheel, invented by W. B. Conyngham and shown in U.S. Pat. No. 1,391,719, comprises two half-wheels with circumferential flange extensions about the shaft. The two halves are bolted radially together through the flange extensions at a hub extending axially away from the wheel. The bolts also lock the wheel in place on the shaft, preventing the wheel from floating along the shaft as is often desirable in modular plastic conveyor belt systems.
U.S. Pat. No. 5,037,356 to Gladczak et al. shows molded plastic split sprocket halves held together by bolts through aligned, diagonal fastener sleeves. The fastening mechanism of the Gladczak split sprocket is not designed for use with thin sprocket wheel disks useful in abrasive environments.
A split sprocket capable of being installed on and removed from a shaft in a direction perpendicular to the shaft is shown in U.S. Pat. No. 5,279,526, filed Dec. 19, 1992 in the name of James O. Gundlach and assigned to the assignee of this invention. The Gundlach sprocket halves are retained by bolts through axial overlapping flanges of the joined halves. While such sprockets are excellent for servicing in tight quarters, they must be thick enough to provide strong overlapping flanges. If made of metal, such sprockets are heavy; if made of plastic, such sprockets are susceptible to wear in abrasive environments.
Thus, one object of the invention is to provide a long-life sprocket for use in abrasive environments.
U.S. Pat. No. 4,049,112 to W. Tyslauk shows a split sprocket for a chain drum. The sprocket comprises two identical sections each having axial annular shoulders. Locking disks, which have axially extending lips embracing the annular shoulders of the sprocket sections, and other locking hardware are required to hold the sprocket sections together. Such an assembly is not readily separable into two mating sprocket halves.
A conveyor chain sprocket in which a sectional tooth rim is clamped between two hub portions on a drive shaft is the subject of U.S. Pat. No. 5,061,225 to Jorgen Draebel. Although Draebel's hub portions, which are connected against each other, can be loosened to remove worn tooth rim sections without disassembling the shaft, replacement or installation of the circular hub portions requires that the shaft be disassembled. Furthermore, the hub portions and the locking hardware must exert enough pressure on the tooth rim sections to prevent them from separating under load.
Chain-drive sprocket assemblies shown in U.S. Pat. No. 1,201,748 to T. C. Luce and others shown in U.S. Pat. No. 1,835,406 to K. F. J. Kirsten comprise stacks of similar, staggered sprocket wheels. Sprocket assemblies comprising connected gangs of individual laminar sprocket wheels spaced apart along a drive shaft are shown in U.S. Pat. No. 5,170,883 to Brent A. Ledet et al. and assigned to the assignee of this invention. The ganged Ledet sprockets are particularly useful in modular plastic conveyor applications requiring frequent cleaning. All of these stacked or ganged sprocket assemblies can be removed and installed only by sliding them along the shaft and on and off the ends of the shaft, an operation that can be inconvenient, time-consuming, and costly.
Thus, a further object of the invention is to simplify the replacement of sprocket assemblies on the shafts of linked conveyor belt systems.